Too annoying to be much fun
It's fun to a certain extent, but a little too tough to be enjoyable. This was mainly because it wasn't always clear who was bigger or smaller than you, and the boss screens usually rapidly became too crowded with bigger creatures making avoidance impossible and death almost inevitable. It's not exactly fun sitting around waiting for a fire bonus to shoot the boss and then to see it drift past inaccessible because of the boss or huge creatures being in the way. If it was a console game I think I'd have thrown it against the wall by now.